This invention relates to pulleys and, more particularly, to pulleys having integral hubs that are formed from sheet metal blanks. There are a variety of techniques employed in the fabrication of pulleys having hubs. One such technique involves spin forming the web and rim from a sheet metal blank, machine forming a hub, and attaching the hub to the web by welding or brazing. While this technique facilitates the formation of a hub having a complete shape, the separate operations involved add significant costs to the pulley.
More recent techniques involve radial displacement of metal from an annular sheet metal disc to integrally form a hub having a blind bore therein. Such a technique is described in U.S. Pat. No. 5,987,952. According to that patent, a sheet metal disc having a center hole therethrough is provided. The disc is placed on a powered headstock mandrel having a vertical center pin which extends through the center hole of the disc. A stepped mandrel having an axial bore therein is telescoped over the headstock pin so that the end face of the mandrel engages an annular portion of the disc immediately surrounding its center hole. A shaping roller is pressed against a face of the spinning annular disc and is moved progressively radially inwardly to displace a portion of the metal in the form of a traveling annular wave while thinning the disc. The annular wave is pressed against the rotating stepped mandrel. The wave which is pressed against the mandrel forms the hub, and the annular inward portion held by the mandrel becomes a blind bore for the hub.
A disadvantage of the above technique is that the tooling and the initial hole size in the metal blank dictate the diameter of hubs produced thereby, thus limiting the process to production of blind bore hubs having a single set of given dimensions; i.e. hub diameter and bore opening diameter. If it is desired to change the size of the hub and/or the diameter of the blind bore opening, it is necessary to blank out the disc initially with the desired blind bore diameter and/or change the mandrel tooling. It is therefore desirable to provide a technique for producing a pulley hub having a blind bore wherein the diameter of the hub can be set by a simpler and less expensive change of tooling, and wherein the diameter of the bore opening of a blind bore can be adjusted without having to provide sheet metal blanks with center openings of varying diameter to accommodate different diameter blind bore openings.
This invention provides a method of forming a hub having a blind bore integrally with a solid circular disc that can be used to form a pulley. The internal diameter of the hub and the internal diameter of the blind bore opening can be easily varied. According to this invention, a solid circular disc is provided. The disc is placed in a recess in a headstock mandrel and is held at its center by a hub-forming mandrel having an outside diameter corresponding to the inside diameter of the hub to be formed. The disc is spun by the headstock mandrel while a shaping roller engages an edge portion of the disc and is moved progressively radially inwardly toward the center of the disc. The roller is also moved downwardly at a slight angle to move metal in the form of a wave toward the center of the disc. The wave is pressed against the hub-forming mandrel to form the hub.
The shaping roller is removed and a final finishing roller is pressed against the hub to finish forming the hub. The disc containing the integrally formed hub is removed from the headstock mandrel and a center hole is punched to conform to the desired bore opening diameter of the blind bore.
Thus it should be appreciated that a wide variety of hub diameters can be produced by replacement of a single, relatively inexpensive hub-forming mandrel, and that a wide variety of bore opening diameters can be incorporated therein by using punches of varying diameters.